Personal portable, intrusion alarm devices have become relatively popular in recent years. They can be used in one's permanent place of abode, in place of, or as a supplement to a permanently installed alarm system. Such portable alarm devices are widely used to provide a warning of unauthorized intrusion in places other than one's permanent home, such as hotel rooms, vacation homes, motor homes and boats, to mention a few examples.
There are several different types of intrusion alarm systems. Some have sensors that are fastened to a door or window which sound an alarm when the door is opened or the window raised. These systems typically require that the sensors be properly installed or attached to the window or door as the case may be. Other systems utilize electromagnetic fields or ultrasonic transducers, for example, that detect the presence of a person in the room. This type of system is also effective for certain applications, but only in areas where persons or animals are not normally present.
More recently, portable systems have been proposed that are sensitive to noise and/or to changes in ambient air pressure. Such systems have been found effective for certain applications but tend to be prone to false alarms, such as those caused by traffic noises, barking dogs, or other unexpected, but harmless, noises, for example.